Digesting process and apparatus



June 18, 1940. r l.. DUNBAR `DIGESTING PROCESS AND APPARATUSl l Filed July 2, 1936 Plantea :une is, i940 t 2,205,374

UNITED STATES PATENT OFFICE 2,205,874 nIGEs'rmc rnocEss AND mamans Thomas L. Dunbar, Watertown, N. Y., assigner to Chemipulp Process, Inc., Watertown, N. Y., a corporation of New York Application July 2, 1936, Serial No. 88,639 Claims. (Cl. 92-7) This invention relates to improvements in di- A gasand steam conducting pipe Ila extends gesting systems and more particularly to specific from the top of the degassing tank and joins a improvements in the digesting processes and appipe I9 provided with an automatic relief valve paratus disclosed in my Patents 1,955,057 dated I8, set to open at any desired pressure, say 10 to 5 April 17, 1934, and 2,041,597, dated May 19, 1936. 15 pounds per square inch. The pipe I9 leads to 5 The primary purpose of. the invention is to proa raw acid eductor into which the raw acid is vide a novel process and apparatus for washing introduced through a Jpipe 20a. A drop leg `2I the stock and emptying the same from the diextends from the eductor into the lower portion gester and for recovering gases and heat units of. the acid storage tank.

1o released in such operations. 1 The degassing tank 2 has a liquid outlet 2a at 10 With the foregoing object outlined and with its bottom leading to a control valve 22 arranged other objects in view which will appear as the in a liquid conducting pipe 23 that discharges description proceeds, the invention consists in into one end of the heat exchanger 3. This liquid the novel features hereinafter described in conis discharged'from the other end of the heat exl nection with the accompanying drawing, and changer through an inverted U-shaped pipe 24 15 more particularly pointed out yin the appended leading the liquid to a sewer or by-product plant. claims. The bend at the top of the pipe 24 may be pro- The drawing is a diagrammatic side elevation vided with a valve controlled vent 48 leading to of the improved apparatus employed in practhe atmosphere.

20 ticing the new process. Acid from the tank 4 can be discharged 20 In the drawing, I designates an `ordinary sul-- through avalve 25 and pipe 26 into a cold acid phite digester of which there may be one or sevpump 21 which forces the acid through a pipe eral in a plant. Although only one is illustrated,. 28 leading to a coil 29 arranged in the heat exthe present invention may be employed with one changer 3. Acid heated in this way passes 25 or more such digesters. 2 is a degassing tank; through the pipe 30 and enters the top of the 25'y 3, a heat exchanger; 4, an acid storage tank; accumulator eductor 9a.

A and 4a, a pressure accumulator; one or more of In order that water may be introduced into the which may be used depending on the capacity top of the digester, the latter is provided with an of the particular plant. intake pipe 3l having branches 32 and 33 pro- 30 Each digester is provided with a strainer 5 vided respectively with control valves 34 and 35. 30 communicating with a, tting 6 having a valve 1 The branches permit the water to be introduced to control the flow of. fluid from the digester into into the very top of the digester or at a point a pipe 8 leading to a high pressure header 9 which somewhat lower down. The lower end of the discharges into an eductor 9a communicating digester is provided with a pipe 36 having With af drop leg 9D, joined t0 a SeCOnd edllCtOl 9C branches 36a and 36h, the former being provided 35 for leading the iluid into the lower portion of with a valve 31 leading to a trash pump 38 which the accumulator 4a. discharges into a pipe 39 leading to a stock chest A side relief branch Ill leads frOm the upper (not shown). A water pipe 4I is provided with POIOII 0f the digester t0 the Pipe s and SPIO- a control valve 40 and leads into the pipe 39 to o vided with a control valve II. aid in removing the stock from the digester. kA 40 A pipe 60 Connects the 10We1' ends 0f the acpipe 43 leads water to the pipe 4I and also to the cumulator and the digester and is provided with pipe 351, and it is provided with a valve 42 for an interposed Pump s' for forcing hquor frm. controlling the water conducted to the branch the accumulator 11,1150 the digester: A valve 62 1s 36h. The water pipe 43 has another branch 43a 45 arranged in the plpe for controumg the w of leading to a. pipe 44 which discharges into the liquor through the same' fitting 6 for the purpose of cleaning the strainer I val I2 co'lgngwlsfgi mgl; sfl pig; I 3 5; and the pipe 44 is provided with a control valve s that discharges into a header I3a accommodat- 5- The to? of Phe dlgestefhas a Vent P196r l ing the various digesters of the plant; and a pipe through Whlch all may be dlSChalged t0 the gw- 50 |:b1eeds from the header te e. pump u which is mosphere w means 0f valved branch 4ta: Pme used to force liquids through a pipe I5 having a, 46 also has a control valve 46h and 1t 1s Joined by differential pressure valve I6. This pipe termia branch 46c to the high pressure header 9. A nates in a spray head I1 within the upper portion valve 41 is interposed in the b ranch.

of the degassing tank 2. The digester is provided with a conventional 55 gauge glass 5U and the degassing tank is provided with a similar gau'ge glass 5|.

As above mentioned, the present application is especially concerned with'waste liquor drainage from each digester through the header |3a which assists in conveying the waste cooking liquor from the digesters to the degassing tank.

'I'he normal operation is as follows: The filling of the digester with chips and acid; pumping a hydraulic pressure on the digester and precirculation of. the accumulator acid through the digester back to the accumulator are as disclosed in my above-mentioned Patent 2,041,597. When precirculation of the accumulator acid through the digester is completed, as indicated by the same temperature readings in both the upper and lower thermometers of the digester, the valve 62 inthe acid filling line is closed and the filling pump 6| stopped. Valve l is immediately opened, valve is usually closed but may be left open if conditions warrant, and liquor is forced out of the digester by the hydraulic pressure through 5, 6, 1, 8 and 9 into the eductor 9a where it commingles with the raw acid liquor forced by the cold acid pump 21 from the storage tank 4 through the heat exchanger and pipe 30. The mixture travels through the drop leg 9b and eductor 9c into the lower portion of the accumulator 4a. Meanwhile the entrained air and gases pass off the digester through` the valved branch 46c into the high pressure header 9 in the same manner as the liquor, explained above. After a short time interval, which varies with the size and type of. digester, high pressure developed, etc., steam is admitted to the digester in the conventional way and the liquor level is lowered to the desired elevation. Digesting temperature and pressure is quickly reached, due to the uniform moisture content of the chips at a high uniform temperature, resulting from the precirculation of a large volume of hot accumulator acid through the digester mass. Again, when the digester goes on side relief to lower the liquor level due to steam condensate value, valve 'l is opened and the liquor is forced by the digester pressure through 5, 6, 1. 8, 9, 9a, 9b and 9c into the accumulator.

The draining of the liquor in this manner produces several benecial results. It removes the cooler liquor from, the dormant areas of the digester, which occur at the lower steam line and thus permits hotter liquor to enter these areas. Therefore, circulation in the digester is greatly facilitated and an improved uniform quality pulp is produced in less time and with a saving in steam and chemicals. This improvement in quality also assists greatly inl emptying the digester of stock when cooking is completed. Furthermore, the quality of the pulp is improved as there are less undercooked and overcooked chips, and a consequent reduction in rejects thus increasing the yield. This results in a saving in time, steam and chemicals as the digester contents will be in a more uniform condition, as to temperature, acid concentration, moisture content of the entire mass, resulting in more uniform digestion. Emptying the digester contents at the end of the oook will also be made easier due to uniform moisture conditions and more uniform cooks.

When cooking is completed the remaining gases in the digester are vented through the pipe 46 to the low pressure header, not shown herein but illustrated in my Patent 2,041,597, which leads to the recovery tank. The digester pressure is thus lowered to correspond with that of the atmosphere. at which time valve I2 is opened to allow the liquor to drain through the strainer I into the header I la from which it is y erably set so as to maintain any suitable pres sure in the tank 2, for example a pressure from 10 to 15 pounds per square inch,

Due to the eductor 20, the hot gases released from the tank 2 are absorbed in the cold acid passing to the tank 4.

The waste liquor after being degassed in the tank 2 is forced through 2a, 22, 23, I and 24 due to the static head or static head and gas pressure in the tank 2 or by means of a pump (not shown). Of course, the hot liquor in passing through the heat exchanger will heat the acid liquor passing through the coil 29 and after being deprived of its heat units the waste liquor will be discharged through the pipe 24 to a sewer or by-product plant for further treatment.

As the inverted U tube 24 extends a considerable distance above the heat exchanger 3, the column of liquor in such tube will put a back pressure on the heat exchanger.

The heat units of the waste liquor, imparted to the raw acid liquor in the heat exchanger 3 will, of course, preheat the liquor passing to the accumulator eductor 9a, and these units will be carried into the accumulator for pre-conditioning the acid liquor therein. Of course, if it is not desired to preheat the cooking liquor in this way, the waste acid liquor may be cooled by passing water or the like through the heat exchanger coil.

While liquor is being drained from the digester, water is introduced into the top of the latter through 3|, 32 and/or 33 to displace the drained liquor and wash the stock, and when the water has entirely displaced the liquor which may be determined by the gauge glass 58, the valve |2 will be closed. Then valve 31 is opened and digester contents are forced out by the stock or trash pump 38 through 36, 36a, 3l and 39 into a stock chest (not shown). Valves 40 and 42 may be opened if desired and valves 44 and 45 may be left open to assist in washing and pumping the contents out of the digester.

After the contents have been removed, the strainer 5 may be cleaned by introducing a stream of water into the strainer through the valve 45. Of course, strainers of any type or style may be used and they may be located in any position in the lower cone, above the lower steam line, or as a separate fitting attached to the bottom flange of the digester. In other words, any of the conventional strainers may be employed.

The herein described and illustrated embodiment of the invention has given satisfactory results, and it will be obvious to those skilled in the art, after an understanding of my invention, that other changes and modifications may be made without departing from the spirit and scope thereof, and it is intended that all features contained in the above description or shown in the drawing shall be interpreted as illustrative and not in a limiting sense.

What I claim and desire to secure by Letters Patent is:

1. In a process of the character described illling a digester with ilbrous material and acid liquor, pumping a hydraulic pressure on the digester and precirculating acid liquor from the digester through an accumulator and back into the digester, continuing such precirculation until the temperature readings at the top and bottom of the digester are substantially equal, then discontinuing the pumping and discharging liquor from the digester through an eductor into the accumulator. discharging gases from the top of the digester while the liqour is discharging and feeding said gases into the accumulator, and mixing raw acid liquor with the digester liquor in the eductor while the last-mentioned liquor is on the way to the accumulator.

2. In a process of the character described nlling a digester with .fibrous material and acid liquor, pumping a hydraulic pressure on the digester and precirculating acid liquor from the digester through an accumulator and back into the digester, continuing such precirculation until liquor,

the .temperature readings at the top and bottom of the digester are substantially equal, then discontinuing the pumping and discharging liquor from the digester through an eductor into the accumulator, discharging gases from the top .of the digester while the liquor is discharging and feeding said gases into the accumulator. mixing raw acid liquor with eductor while the last-mentioned liquor is on the way to the accumulator, and subsequently admitting steam into the digester.

3. In a process of the character lling described pumping a hydraulic pressure on the digester and precirculating acid liquor irornthe digester through an accumulator and back into the digester, continuing such precirculation until the temperature readings at the top and bottom of the digester are substantially equal, then discontinuing the pumping and dischargingliquor v i tank through -the`heat exchanger for veecting from the digester through an eductor into the accumulator, discharging gases from the top of I' the digester while the liquor is discharging vand feeding said gases into the accumulator, mixing raw acid liquor with the digester liquor -in the eductor while the last-mentioned liquor is o'n the way to the accumulator, and subsequentlyv adlowering the mitting steam into the digester and liquor level in the latter to a desired elevation.

4. In a process or the character described lesdwaste acid liquor from the lower portion of d tank at the end of a from the waste liquor in ing a digester to a cook, separating gases said tank, absorbing said gases in raw acid liquor,

and then heating the last mentioned liquor by heat exchange with the mst-mentioned liquor.`

5.In a process of the character descri passing waste acid liquor from the lower portion of a digester at the end of a cook into a dng tank, separating gasesl from the liquor under thedigesterliquorinthe` a digester with iibrous material and acid the digester until superatmospheric pressure of approximately: ten

to ilfteen pounds perv square inch, and absorbing said gases in raw acid liquor.

6. In a process of the character described passing waste acid liquor at the end of the cook fromv the lower portion of a digester into a degassing tank, separating gases from the liquor in said tank, introducing said gases into an eductor having a drop leg and also introducing raw acid liquor into said eductor andthereby absorbing the gases in the raw acid liquor, and then heating said chamber and discharging 'said gases into an.

eductor having a drop leg, and introducing `vraw acid liquor into the eductor and thereby absorbing the gasesin theraw acid liquor.

v8. In aprocess of the character described passing waste acid liquor at-the end ofthe cock from the lowerportion of.a dlgesterintoa degassing vtank maintained under superatmospherlc pressure-I separating gases from the `vliquor i'njl said tank, releasing the pressure on thegases, and

then absorbing the gases in raw acid liquor.

9. In an apparatus of the character described a' A `degasifying chamber, a-heatexchanger and a .raw acid-storage tank,.a p'ipefor leading waste acid liquor from the de'gasifying chamber into the heatexchangena pipe for 'discharging waste acid: liquori'rom the heat vexchanger and provided.'-

with means for maintaining--, aback pressure on the heat exchangenan'eductor, means for leadthen circulating hot acid liquor through the accumulator to the digester and back to the aclcurn'ulatorauntil the temperature of the digester is substantially the same throughout the digester, stopping the circulation of the liquor and then discharging liquorv from the digester until the liquid level of thev liquor in the digester falls to a predetermined elevation, admitting steam into the digesting temperature and pressure are reached, then discharging acid liquor from the bottom portion of the digester and mixing it with raw acid liquor, and finally introducingthe mixed acid liquor into the accumulator.

` THOMAS L. DUNBAR.

, ing gases fromthe degaslfying chamberv to saidl material, illling Bil 

